MOVEMENT AND SENSATION AS TEST OF ANIMALS. 21 



of carbonic acid goes on. In plants, therefore, together with 

 the characteristic deoxidation process, there is always found a 

 process of oxidation analogous to that occurring in animal me- 

 tabolism; by which a part of the assimilated substances is again 

 destroyed. The growth of plants is impossible without the con- 

 sumption of oxygen and the production of carbonic acid. The more 

 energetic the growth, the more oxygen is consumed, as indeed the 

 germinating seed or the quickly unfolding leaf and flower buds 

 rapidly consume oxygen and excrete carbonic acid. In this con- 

 nection should be mentioned the fact that the movements of proto- 

 plasm depend upon the inspiration of oxygen. The production of 

 heat (in germination), also of light (Agaricus olearius) is accompanied 

 by an active consumption of oxygen. Finally, there are organisms 

 (yeast cells, Schizomycetes) which indeed manufacture both nitro- 

 genous and albuminous compounds, but do not assimilate the carbon 

 of carbonic acid, but rather derive the necessary carbon from pre- 

 pared carbohydrates (Pasteur, Cohn). 



5. Voluntary movement and sensation, according to the common 

 view, is the chief characteristic of animal life. Formerly, the power 

 of free locomotion was looked upon as a necessary property of 

 animals ; and as a consequence of this the fixed colonies of Polyps 

 were considered to be plants, until Peyssonnel brought forward 

 proof of their animal nature, a view which by the influence of the 

 great naturalists of the last century has gained general recognition. 

 More recently, on the discovery of the existence of motile spores 

 of algse, it was first recog- 

 nised that plants also, 

 especially at certain stages 

 of their development (fig. 

 9), possessed the power of 

 free locomotion, so that 

 we are compelled to direct a ^, 



our attention to the signs v j ^jjj&j? \ 



by which the voluntary FiG>9 _ Zoosporeg>a|0fp ^ flrKm;6>of ^ 



nature Of the movement of Ulothrix; d, of Bedogonium; e, of Vaucheria 



can be decided for a dis- 



tinction between the respective movements of animals and plants. 

 As such for a long time was regarded the contractile nature of the 

 movement as opposed to the uniform movements of plants carried 

 out with rigid bodies. 



In the place of muscles, which as a special tissue are absent in the 



